This application claims the priority benefit of Taiwan application Ser. No. 90/109,497, filed Apr. 20, 2001.
1. Field of Invention
The present invention relates generally to a spraying method of a dispense system. More particularly, the present invention relates to a spraying method of a dispense system that can prevent residue from occurring.
2. Description of the Related Art
The inventive method is applied in a post develop dispense (PDD) process to serve as an example in order to describe the inventive technique.
The fundamental processes of photolithography consist of coating, exposing and developing. In a common use such as a positive photoresist type, the main characteristic of the positive photoresist is to utilize a chemical reaction between a developer and an exposed photoresist layer on a wafer in order to remove the photoresist layer. The unexposed photoresist layer is defined by patterning. In order to have an in-line type of fabrication, a spray/puddle method is generally used for the photolithography fabrication. The spray/puddle method comprises spraying the developer from a spinner onto a surface of a wafer. While the wafer is in a stationary status, a puddle process is carried out. Further, after cleaning the wafer with pure water, a spin-dry process is followed to dry the wafer. Thus the photolithography process is completed.
However, in the above-described process, a portion of the photoresist layer is etched improperly during the etching process. Thus, for a high-density product, a PDD process is added after the photolithography process. The PDD process is carried out before cleaning the wafer. When the wafer is spinning on a machine, a certain amount of developer is sprayed onto the surface of the wafer in a short period. By utilizing the etching effect of the developer plus the spinning force, the portion of improperly etched photoresist layer can be re-etched and cleaned. The cleaning process is carried out by spraying pure water onto the wafer to wash away the residue and developer, and next the spinning-dry process is carried out to dry the wafer.
In the present industrial technology, the above-mentioned photolithography process is carried out automatically by an automatic machine with a mechanical arm. Since the machine is utilized for several steps of the photolithography process, the mechanical arm will return to its home position after completing a spraying process of the developer. The remaining fluid of the developer in the tube will drop onto the wafer due to the movement of the mechanical arm. Since the cleaning process of the PDD process is already completed, the excess drops of developer on the wafer will cause a portion of the wafer to be over-developed.
A conventional method of solving the problem of excess developer is to supply a certain amount of developer during a short period. A suck back process is carried out after the developer supply is switched off, and the remaining fluid in the tube is suck backed by a suck-back valve. However, a capillarity effect will cause a void to occur when the fluid supply is closed rapidly. That is, when the suck back valve retrieves the fluid back, the void and some drops of the developer that are still adhered on the inner surface of the tube will occur in the tube. Those excess drops of developer will either fall onto the wafer or dry out into residue, which can block off the flow of the fluid in the tube. The excess developer can also cause a portion of the wafer to be over-developed.
The portion of the wafer that is over-developed can not be inspected by human eyes. Thus, the defected wafer is usually carried to the next step of the process. During the etching process, the etching reaction in the over-developed portion is aggravated and cannot be controlled, consequently damaging the whole wafer and increasing the production cost.
The present invention provides a spraying method of a dispense system that can prevent the formation of residue. The dispense system of the present invention utilizes a buffer tube with a pin hole to refill a void and prevents fluid from adhering on the inner surface of the tube. The buffer tube supplies the fluid through the pin hole to the void because the pin hole has a very small diameter; thus, the void is refilled slowly with a very small amount. Once the level of the fluid reaches a certain level, the main tube will stop supplying the fluid, and a suck back valve will open to suck back the fluid very slowly so that no void or fluid will adhere on the inner surface. Thus, no residue will form, and no excess fluid will fall onto the wafer.
The present invention further provides a main valve together with the suck back valve to supply the developer to the wafer, wherein the main valve and the suck back valve can control a precise amount of developer that is sprayed onto the wafer. The buffer tube further comprises a buffer valve, which is utilized together with the pin hole to refill the void formed in the tube in such a manner that the void can be refilled. No residue forms on the tube, and no excess developer falls onto the wafer. Furthermore, the present invention can accurately control the precise amount of developer that is sprayed onto the wafer.
Both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as claimed.